In the world of competitive swimming such as Olympics in which swimmers compete to reduce the time by 1/100 second, resistance that occurs between a swimsuit and water (hereinafter referred to as “water resistance”) is a big problem. For example, in the case of a male freestyle top swimmer who swims 100 m in 50 seconds to 47 seconds, the water pressure on his body is as high as 10 kgf (≈98.1 N) or more. In such circumstances, development of a material for swimsuits with less water resistance will lead to an improved record of swimmers.
Meanwhile, in the long history of development related to materials for swimsuits for competitive swimming and to swimsuits, swimsuits for competitive swimming in which swimmers compete in swimming speed have been sewed to fit using a stretch knit because ease of movement in swimming is of most importance. Further, swimsuits made of a knit having fine stitches and reduced knit surface roughness have been produced, the swimsuits being obtained by reducing the total filament fineness of synthetic fiber multifilament yarns used for a knit material for swimsuits or by increasing the number of filaments while reducing the monofilament fineness of the synthetic fiber multifilament yarns to reduce the water resistance of the swimsuits.
However, such knit swimsuits, though they are easy to move with and cause relatively small water resistance, are prone to damage such as pilling, irregular fuzz, or breakage of the swimsuit surface because they are made by knitting thin yarns or yarns having a small monofilament fineness and a large number of filaments, and tend to have a shorter usable lifespan. In addition, because of the larger number of filaments and their small monofilament fineness, the knit swimsuits are likely to be less high-quality: for example, the color development ability decreases.
Further, a swimsuit made by applying an aqueous solution of a high-molecular-weight linear organic polymer to a fiber surface has been proposed (see JP 01-213403 A). The swimsuit can reduce water resistance due to application of the Toms effect and is suitable particularly for competitive swimming. However, since the swimsuit is made by applying an aqueous polymer solution to a swimsuit surface, it is likely to have such a fundamental problem that the polymer dissolves in water to pollute a pool and, at the same time, result in poor performance durability.
Further, there is a swimsuit obtained by calendering one surface of a knitted fabric with heat and pressure to smooth the one surface of the knitted fabric to reduce water resistance, but its performance is still not satisfactory.
Further, a knit (see JP 08-311751 A) and a competitive swimming swimsuit (see JP 09-049107 A) obtained by smoothing a knit surface to reduce water resistance without impairing the ease of movement in swimming and providing water-repellent parts and non-water-repellent parts and have a prescribed elongation have been proposed. However, they are still not sufficiently satisfactory.
Meanwhile, in an attempt to alleviate the discomfort associated with a cold body, a texture obtained by providing a water-repellent finish on the whole surface of a knit or cloth comprising polyurethane elastic yarns has been proposed (see JP 55-026243 A). The cloth has the effect of alleviating the discomfort associated with the cold during wear because the polyurethane elastic yarns are not deteriorated by chlorine in a pool and the swimsuit itself does not absorb much water. Therefore, this technique does not involve an idea of reducing the water resistance that occurs between water and a swimsuit.
In recent years, a swimsuit for competitive swimming intended to control a turbulent flow that occurs in swimming and exert a straightening effect by providing a water-repellent finish on the surface of a knit and also providing groove portions in which a plurality of fine grooves are formed along the body length has been proposed (see JP 2000-314015 A). Further, a swimsuit for competitive swimming intended to exert the effect of reducing the water resistance between water and the swimsuit by sticking a panel made of a polyurethane sheet material on the trunk region, chest region, femoral region, or the like of the swimsuit made of a cloth material and reducing the shape resistance by suppressing the irregular shape of a body by tightening the body been proposed (see JP 2008-150767 A). However, these swimsuits also have problems such as difficulty in putting on and taking off, time-consuming production, and the like, and are still not sufficiently satisfactory.
Further, using a stretch cloth having a low basis weight and a high elasticity that a knit material cannot achieve for a swimsuit has also been proposed (see JP 2010-138496 A). However, this technique does not involve an idea of reducing the water resistance between water and the swimsuit.
Meanwhile, in the field of ships different from swimsuits, studies to reduce the friction resistance between water and a ship using microbubbles (hereinafter “microbubbles”) have been conducted since 1990's. Specifically, they are studies of a technique for reducing the friction resistance of water that the wall surface of a substance encounters by forming a thin air layer by injecting microscopic bubbles (microbubbles) into a boundary layer between water and the substance, the boundary layer being along the wall surface of the substance moving forward in water.
In the technique for developing ships, a field of specific developmental use, ships that are large and move forward slowly, in particular, large tankers that play a major role in marine transportation and the like are said to be more suitable for application of microbubbles, and practical application thereof have actually been achieved. This has reduced the power to drive a large ship and facilitated increased speed.
The mechanism of reduction in friction resistance by microbubbles has not been definitely established yet. One possible mechanism is the density effect; that is, the density of air is as low as about 1/1000 of the density of water and, therefore, bubbles gather near the surface of a substance and are distributed in a layer, which reduces the friction of water. Another reduction mechanism is the turbulent flow-preventing effect; that is, bubbles prevent the turbulent flow in the boundary layer, a primary cause of friction. It is said that the synergistic effect of these two mechanisms provides the effect of reducing the friction drag between water and a ship by microbubbles.
For a specific structure of a submerged portion of a ship, a microscopic irregularly-shaped layer is formed on the surface of the submerged portion by painting, and the irregularly-shaped layer is coated with a water-repellent material. Meanwhile, compressed air is jetted from a compressor installed inside the ship through a thin nozzle to the outside of the ship (the surface of the irregularly-shaped layer coated with the water-repellent material). This will form a thin air layer of microbubbles on the periphery of the submerged portion of the ship (Nagare 20 (2001) 278-284, Feature article: Fluid Mechanics in the Ocean “Reduction in friction drag of ship by microbubbles”).
However, no case has been found in which the idea of such a technique for reducing the friction drag between water and a ship by microbubbles is applied to a swimsuit.
There is thus a need to overcome the defects of a swimsuit made of a knit or cloth for swimsuits as mentioned above and to provide a cloth for swimsuits that satisfies various properties (elongation, basis weight, thickness, ease of movement, durability in use, mechanical strength, aesthetics, and the like) required for a material for swimsuits, and at the same time have a texture design that generates microbubbles by which water resistance can be more reduced than before when a swimmer swims wearing a swimsuit made of the cloth, and a swimsuit made thereof.